This invention relates to a process and system for molding soles on to last supported shoe uppers, wherein the spatial coordinates x, y, z of the molding-on region of the shoe upper periphery are measured, and a processing tool such as a roughening element for the shoe upper surface or an adhesive applicator or a deburring element is guided along a curved line determined by the spatial coordinates. A shoe molding apparatus is located at each of a plurality of equally spaced apart shoe molding stations on a circular turntable installation, each such apparatus comprising a last supported shoe upper, a movable bottom stamp and a mold cavity delimited by the bottom stamp and a pair of opposing lateral side mold elements closing against the periphery of the shoe upper. Upon incremental movement of the turntable, the cavity at each station is injected with low viscosity material such as polyurethane, thermoplastic material, rubber, for molding a sole on to the shoe upper. The peripheral edge of the shoe upper is thereafter freed of extrusion burrs.
During the process of molding soles on to last supported shoe uppers, adherence of the molded sole to the shoe upper can be improved if in the region to be soled the surface of the shoe upper is first roughened and, if desired, applied with an adhesive. Only a small portion of defective sole attachments are the result of sole adhesives used such as polychloroprene or polyurethane adhesives. Instead, such defective sole attachments are known to result from careless or inadequate Processing to assure adherence of the molded sole on to the shoe upper.
Tools used for roughening comprise wire brushes, roughening discs and roughening rolls having steel wires embedded in a rubber holder, grinding stones and sanding belts. Machine roughening, as well as manual roughening, requires that the tool be guided with precision to avoid damage to the surface material of the shoe upper. An important factor during the roughening process is also the pressure applied by the tool. Roughening must be carried out in such a manner that the surface of the shoe upper is cleaned of foreign substances such that the outer surface layers are removed exposing a cleaner layer of material with which the sole can permanently adhere, if necessary using an intermediate layer of adhesive.
Also, roughening brushes can be guided about the shoe periphery by following a pattern tat matches the last which is being used so as to automate the roughening process. The drawback is that this requires a separate pattern for each last thus resulting in an increase in time and material cost. Also, guiding the roughening tool in such manner does not take into consideration any unevenness or profile imperfections of the shoe upper material or of the last.
During application of the adhesive it is important that the adhesive layer on the surface of the shoe upper be precisely positioned and that its thickness ranging from 20 to 30 microns be as uniform as possible. If the adhesive layer is thicker the layer can crack which may result in the adhesive layer peeling off. Moreover, a too thin layer of adhesive reduces the adhering effect required for the molded on sole. Thus, automation of the adhesive layer application is limited without introducing more extensive and costly adhesive applying operations. This limitation applies to the roughening procedure as well.
Also, the sole extruding or molding of polyurethane presents problems due to its low viscosity. To assure that the molded sole is appropriately sealed to the shoe upper, the Polyurethane is injected into the mold cavity which is larger than that of the sole to be extruded, whereby the polyurethane is foamed. It is then compacted to form the sole. Formations of injection molds which largely prevent expulsion of material are disclosed in West German patent Nos. 20 22 118 and 20 48 596. Since the formation of burrs at the edge of the sole cannot be completely prevented, the burrs must be removed after the sole material cures. This also applies to shoes having multi-layered soles disclosed in the West German patent No. 22 41 493. During the first work cycle of the process therein disclosed the outer sole is extruded into the mold cavity, formed by side mold elements, a bottom stamp and a counter stamp, such that the mold cavity size is not reduced until the polyurethane has been foamed to the size of the inner sole. The counter stamp is replaced by the last supported shoe upper and the inner sole is extruded in a corresponding manner or compression molded by reducing the size of the mold cavity.